It is now a known technology to incorporate a high-dielectric layer into a multilayer printed circuit board etc. to obtain a function of condenser or the like. The high-dielectric layer can be prepared by, for example, adding inorganic powder of high dielectric constant to a solution obtained by dissolving a thermosetting resin in an organic solvent; impregnating a fibrous reinforcing material such as glass fiber with the solution to make up for the brittleness of the thermosetting resin; and calcining the impregnated material to evaporate the solvent and cure the resin. However, it has been difficult with such conventional methods to obtain a dielectric layer which has a high dielectric constant, generally 20 or more, and which is at the same time thin and has a low leakage current.
Further, various inorganic powders have been used in attempts to obtain a dielectric layer of a high dielectric constant. For example, it has been found that a dielectric layer having a high dielectric constant can be prepared by addition of an inorganic powder, such as of Fe3O4 or a mixture of ZnO and carbon, into polystyrene. However, dielectric layers thus obtained, although high in dielectric constant, have a high dielectric loss so that they generate high heat in an alternating electric field. This heat generation causes deterioration of multilayer printed circuit boards etc. including the dielectric film, and further gives rise to troubles such as breakage of joint by thermal stress. Accordingly, there have been problems of poor reliability and durability of the semiconductor boards.
On the other hand, it is a known method for achieving a high dielectric constant to form a dielectric layer by calcining an inorganic powder of high dielectric constant at high temperatures. However, due to the calcination which should be carried out at high temperatures around 1000° C., this method cannot be applied to uses where a dielectric layer is to be incorporated in a wiring board carrying electronic parts. Thus, it has been impossible to apply this method to versatile uses in the production of various kinds of semiconductor boards.
A screen printing process is a known method for forming dielectric layers. This screen printing process has been unable to deal with difficult demands for accurate pattern position that come from the recent trends of boards toward large size and meticulous structure.
Accordingly, there has been a demand for a photosensitive composition for forming a dielectric which can be calcined at low temperatures to form a dielectric layer that has a high dielectric constant and a low dielectric loss and is patterned with high dimensional precision.